The present invention relates to extracting a solute from a solid material and, more particularly, to extracting oil from oil-bearing foodstuffs.
Many food products contain varying amounts of oil, i.e., liquid triglycerides, which can be extracted as a valuable commodity. Such food products include cocoa and other plant materials, such as oil seeds, cereal brans, fruits, beans, berries, and nuts. There are numerous important commercial uses of the oils derived from such plant materials, such as in cooking, confectionery, cosmetics, pharmaceuticals (as carriers), lubricants, and other applications. In the case of some food products, the defatted food product might also have some commercial or industrial use. Accordingly, numerous processes aimed at extracting and separating such oils have been proposed.
Organic solvents are frequently used as the medium for extracting oil from such food products. In a conventional extraction process, the oil-bearing food product is treated with a suitable solvent, usually a lower carbon alkane, such as propane, butane, or hexane, to extract the oil from the oil-bearing food product. The constituents of the resulting solvent/oil mixture, called a xe2x80x9cmiscella,xe2x80x9d are then separated from one another, typically in a distillation unit. In this way, the isolated oil product can be recovered and the solvent can be recycled.
A common commercial solvent employed is hexane, which, although widely used for the recovery of oils, is not well suited for the recovery of food quality solids. This solvent is considered toxic, and the conditions necessary for minimizing residual solvent in the solids (both high temperature and use of direct steam injection), adversely affect desired properties, such as flavor and aroma. Increasing interest in reduced fat foods has resulted in the increased use of normally gaseous solvents, such as super critical carbon dioxide, liquid propane, and liquid butane for the removal of fats and oils. These solvents, which are commercially in use for the extraction of foodstuffs, are typically used in a batch-type extraction process.
Although continuous extraction provides certain economies, including the ability to use countercurrent flow of solvent, the pressures required present significant technical hurdles. Maintaining a seal between the atmospheric environment and the pressurized vessels is difficult. Dealing with fine particles necessitates either pelletizing a feed stock or complex filtering processes which are further complicated by operating in a pressurized environment. Also, when using normally liquid solvents, certain products create difficulties when preparing the material for extraction.
For example, the preparation of oil seeds for extraction involves rupturing of cells and the production of flakes, pellets or collets to increase surface area, porosity, and facilitate contact and draining of the solvent/oil mixture. However, large particles, such as pellets, although reducing channeling and allowing for improved draining, also inhibit the leaching of the solute from the solid, necessitating a longer extraction time. Other products, such as rice bran, are unstable and subject to oxidation degradation when exposed to conditions, including heat or air exposure, such as are experienced when pelletizing. Also, products that are initially high in oil/fat content, such as peanuts or cocoa beans, after cell rupture, must be further processed to remove a portion of the oil/fat in order to prepare solid pieces for extraction. In other words, with such a high oil content, these products form a flowable mass, a difficult form from which to extract oil using conventional processes.
In summary, several problems exist with current extracting processes which make the process either more difficult, more expensive, or result in poorer quality. Hexane is not satisfactory for foodstuffs when the solids are of interest. In addition, normally gaseous solvents do not lend themselves readily to continuous processes. Moreover, pelletizing can degrade certain products and extend the extraction time for others.
In view of the prior art extraction methods and their shortcomings, there exists a need for an extraction process and system which can be used on a continuous or batch basis and which can be used to extract oil from foodstuffs in a number of forms, including powder. Preferably, the system should be able to accommodate normally gaseous solvents in a continuous process.
In view of its purposes, an embodiment of the present invention provides a process for extracting a solute from a material comprising first mixing a liquid extracting medium with a solid material in an extraction vessel to form a first mass. Next, the first mass is passed through a substantially tubular membrane filter for separating a miscella, which is some of the solute and the solvent from the extraction medium, from a second mass having a reduced solute content and the rest of the solvent. The solvent is then removed from the miscella to isolate the solute and from the second food mass to form reduced solute, desolventized foodstuffs.
According to an embodiment of the present invention, a batch process for extracting a solute, such as oil, from a material, such as oil-bearing foodstuffs, involves first mixing solid foodstuffs and a liquid extracting medium in an extraction vessel to form a first mass, which is passed through a substantially tubular membrane filter for separating a miscella from a second mass, as above. After returning the second mass to the extraction vessel, extracting medium is again mixed with the second mass to form a third mass, which is again passed through the membrane filter for separating a miscella from a fourth mass. The solvent is then removed from the miscella to isolate the solute and from the fourth mass to form reduced solute, desolventized foodstuffs.
According to an embodiment of the present invention, a continuous process for extracting a solute, such as oil, from a material, such as oil-bearing foodstuffs, involves first mixing solid foodstuffs and a liquid extracting medium in a first extraction vessel to form a first mass, which is passed through a substantially tubular membrane filter for separating a miscella from a second mass, as above. The second mass is then mixed with extracting medium in a second extraction vessel to form a third mass, which is passed through a second substantially tubular membrane filter for separating a miscella from a fourth mass. The solvent is then removed from the miscella to isolate the solute and from the fourth mass to form reduced solute, desolventized foodstuffs.
According to another embodiment of the present invention, a system for extracting oil from oil-bearing foodstuffs comprises an extraction vessel, a substantially tubular membrane filter having an average pore size of between 0.1 microns and 10 microns, a separator, and means for removing the solvent from a mass conveyed from the membrane filter. More specifically, the extraction vessel accommodates the mixing of a liquid extracting medium with solid foodstuffs to form a first mass. The membrane filter is coupled to the extraction vessel and serves to separate a miscella from a second mass. The separator is coupled to the membrane filter, receives the miscella from the membrane filter, and serves to remove the solvent in the miscella to isolate most of the oil. Finally, the means for removing the solvent in the second mass to form reduced oil, desolventized foodstuffs might include a heater, a depressurizer, or a baghouse.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, but not restrictive, of the invention.